ERBB2 and breast cancer: Figure 2 shows receptor complexation and phosphorylation by co-immunoprecipitation/Western blotting in the same panel of breast cancer cell-lines used in the VeraTag FFPE assays and there is generally good correlation between the cell lysate and FFPE measurements. In cell-lines with high HER2 expression the ligand-independent dimers constitute a significant proportion of the dimer signal. Additionally, in high HER2 cell lines HRG expression is low [34] suggesting that the presence of HER23 heterodimers is ligand-independent.